Menstruation, or periods, are times when a girl or woman bleeds naturally from the vagina. Periods are a sign of health and show that the body is functioning as it should.

What are periods?

When girls become sexually mature and their bodies become capable of carrying a baby, they begin to produce female sex hormones.

These are naturally occurring chemicals, which control the development of breasts, the growth of pubic and armpit hair and also control periods.

Menstruation, or periods, are times when a girl or woman bleeds naturally from the vagina.

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Periods are a sign of health and show that the body is functioning as it should.

It's a good idea for a girl to talk to her mother about periods, or if this seems difficult or is not possible, she might prefer to speak to a sister, a cousin or someone else she feels comfortable talking to.

What happens in the body during a period?

The female reproductive organs inside a girl's body comprise:

the ovaries, which produce eggs and hormones

the Fallopian tubes, which connect the ovaries to the uterus

the uterus (womb), a muscular organ where the egg can attach itself once it has been fertilised by a male sperm cell when pregnancy occurs

the cervix or neck of the womb, which connects the uterus to the vagina

the vagina attaches to the lower part of the cervix and is the passage that leads outside the body. It permits blood from a period to escape and will enlarge to allow a baby to pass through. It has an important role in sex. The erect male penis is inserted and following ejaculation, sperm is deposited in the lower pocket of the vagina, which then swims through the cervix, uterus and Fallopian tube to find and fertilise an egg.

When a girl reaches puberty, her hormonal cycle starts and it's possible for her to become pregnant.

Oestrogen and eggs are produced by the ovaries. Oestrogen is a natural chemical in the body called a hormone.

It causes the womb lining to thicken to enable a fertilised egg to implant at the start of pregnancy.

The ovaries release a mature egg 10 to 14 days, after the start of a period, this process is called ovulation. Following ovulation, the ovaries switch from the production of oestrogen to progesterone. The egg moves through the fallopian tube.

If the egg is not fertilised, the ovary stops producing the hormone progesterone.

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When the level of this hormone falls, the lining of the womb is shed. This is associated with some blood passing from the vagina, commonly called a monthly period.

This cycle usually takes 28 days, but the bleeding lasts for 5 days.

When do girls begin to have periods?

Periods occur throughout the time a women is fertile and able to have a baby. For the average woman this is from the age of 12 to 55, when the menopause starts.

A number of things can stop the period and menstrual cycle but the commonest reason in young women is pregnancy.

How often do women menstruate?

For the average woman the monthly period occurs every 28 days. The bleeding usually lasts for 5 days.

In the next 9 days an egg is matured and released. If the egg is not fertilised, the progesterone production falls after 7 days, triggering the bleed again.

Although the average woman has a 28 day cycle with a 5 day episode of bleeding, it's not unusual for some girls to notice they have a similar cycle but it may be shorter or longer.

In some instances especially when the cycle starts, they may be irregular. You may find it useful to keep a diary of your period so you know when it will be due and will be alerted if it's late and you may be pregnant.

How do you prepare for your first period?

It's good to be prepared and have some sanitary towels close by for when your period starts.

These are absorbent pads placed in the underwear to minimise any staining of your clothes.

How many you need will depend on how much you bleed, but it's a good idea to always have some spare with you, in case you need to change it and you are not at home.

If you suddenly find you need one, the school nurse or a teacher may be able to help.

In addition to noticing some bleeding, it's common to experience some lower abdominal cramping pain. This is due to the uterus contracting, which is stimulated by the bleeding and start of the period.

What do you do with a used sanitary towel?

Do not flush sanitary towel down the lavatory because they absorb water and may block the lavatory.

To dispose of a sanitary towel, wrap it in some toilet paper and place it in a bag before placing it in the waste bin in the lavatory.

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